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Thursday, September 03, 2015


We smell a sewer odor throughout the house. It is a small, one-bedroom ranch/slab house with one bathroom and no crawl space. The smell is VERY STRONG at the 2 cold air return vents and then when the heat comes on I want to vomit. We have no cracked pipes; we have checked the attic for mold and dead animals. The plumber did the camera inspection and found no water under the furnace or in the air ducts. The plumber says our main clean out was 90 % blocked by tree roots. We have lived here for 10 yrs and have never had this before. Help!


Answer # 1:
It sounds as if you have a tough one on your hands. This really isn't a cleaning problem until you find the source of the odor. Then it may or may not be a cleaning problem. I agree with you, the sewer smell is not good for oneís health and is an indication of a serious problem in the home. Here are some
things to consider:
Basic Odor Control 101. To eliminate an odor problem you need to find and remove the source.
1. Is there a floor drain in or near the furnace? Dry floor drains are often the source of sewer gas, as they need to be used on a regular basis to keep their traps from dying out. Flushing them with a gallon of water every two weeks will do the job. If there is a drain, cover it for a few days and see if the odor goes away.
2. When did the odor first show up? Were any repairs, renovations, or remodeling done around that time? If so, I'd look closely at the area where the work took place.
3. From your comments it sounds as if the source may be in or near the furnace or duct work. Did the furnace guy inspect the heating system with a camera. If not, someone should. That could be the source of the odor from a dead animals. Any pets disappear recently?
4. Does your heating system use the space between the wall studs in some areas of the home as a return air duct. If so, sewer gas may be getting into the wall space from a broken or uncapped pipe and getting sucked into the air handling system.
5. It might be a good idea to open up the wall near the sinks in the home to make sure a previous remodel didn't leave a drain or clean out uncoved in a wall that is now enclosed.
6. If the drainline is plugged 90% with tree roots, it needs to be cleared.
Sewage can't be flowing very well through a pipe that's clogged to that degree. If the problem disappears after cleaning the roots, you can assume that the two problems were connected in some way.
7. There may be a sewer leak or back up that you are not aware of or finding. You might want to have the home inspected with an infrared camera to see if this would identify a wet spot in a wall, floor, or other space which may indicate a possible source of the odor.
Best of luck. Let us know what the source of the odor is once you track it down.
Bill Griffin, President

Answer # 2:
Check closely numbers 3, 6, and 7 above.
You live in a ranch built on a concrete slab. With no basement or crawl space available, the utilities are necessarily buried under the slab. That is where your cold air returns are, as well as the house water coming into the meter inside and the sanitary sewer lines. None of these can be inspected easily for their proximity to one another, but the key is that the cold air vents under the slab are picking up the odor of sewage. Somehow the sewer gas is getting from the sewer lines into the air return.
When the fan turns on for the furnace, it draws air through the returns into the unit to be heated and blown into the rooms. You donít need actual sewage in the return ducts, just the gas to produce the odor. With a fan drawing the air into the furnace, it will pull air from any opening.
Somewhere below the slab, the sewer line and the air returns are close enough to each other for this exchange to take place. A leak in the sewer line may be allowing waste water to accumulate in a pocket under or around the sewer line. This reservoir may, in turn, provide a source of odor for a nearby air return, possibly even allowing seepage into the ducting. I know the camera didnít see any water in the ducts during the inspection, but the warm, dry forced air flowing through the duct would quickly cause a small amount of moisture to evaporate and become part of the airflow.
The statement that there are no cracks in the sewer pipes puzzles me, since any line blocked 80% or more by tree roots obviously has some openings for the roots to grow through to get into the pipe to begin with. With that degree of blockage, I am amazed that any solids are able to reach the septic tank or main sewer line out in the street.
The trench that the sewer line is laid in may be filled with sewage-saturated soil to the point that seepage is occurring into the nearby air ducts. The wastewater is seeping out of the same breaks, cracks, seams, or holes through which the tree roots are getting into the line.
The on and off nature of the problem may be related to water usage that may back up more heavily at some times than at others.
Digging down to allow a visual inspection of the line and the trench it lies in just outside the building where it emerges from the foundation wall may show this condition and release the pressure, allowing the water to flow out from under the slab. In time, this will dry out and the odor will disappear. Start by digging this up to look at it, and do get the lines cleared of roots to prevent back pressure that may be forcing sewer water into the ground under the house.
If the ground is not frozen too deeply, you may be able to get after this soon.
Lynn E. Krafft, ICAN/ATEX Associate Editor